Approach to be used near the borders during various transformations.
Whenever a function needs information not only about an element of interest, but
also about it's neighbors, it will go out of bounds near the array edges,
hence is this set of approaches that specify how to handle such situation.

This is bread and butter of multi-dimensional array indexing. It is unlikely that any of the
functions in this class will be useful to a regular user, unless general algorithms are being
implemented that do span multiple dimensions.